Dual-calendar timestamps for Persian and Pashto

[jamesdonoh]

Is your feature request related to a problem? Please describe. Following the investigation in https://github.com/bbc/simorgh/issues/1567 we have decided to add support for dual calendar (Gregorian and Jalali) timestamps to psammead-locales.

The implementation can reuse some of the code and tests from the legacy moment-ws codebase as it has been extensively validated in production, but it should be reviewed for correctness and modernised/tidied up before being integrated into psammead.

Describe the solution you'd like

• Where possible reuse the existing moment-ws JS code and tests (with appropriate updates/improvements and the addition of any required documentation)
• Add any locale changes (e.g. Jalali month names) to the moment.js locales in psammead-locales - as has already been done for Yoruba
• Re-use jalaali-js for the actual calendar conversion unless there is a more lightweight/convenient alternative (some research needed)
• Demonstrate that only the Pashto/Persian service bundles sizes are increased (by the minimum possible) and other bundles are not impacted

Describe alternatives you've considered See https://github.com/bbc/simorgh/issues/1567

Testing notes

• Full unit test coverage
• Update storybook and relevant documentation

Dev insight: Will Cypress tests be required or are unit tests sufficient? Will there be any potential regression? etc

Additional context Add any other context or screenshots about the feature request here.

[ibMadbouly]

the dual calendar conversion is waiting on issue #1788